1. Field of the Invention
This invention is directed to the field of planar magnetic acoustic transducers and particularly to the use of angled magnetic motor structures for more uniformly driving electrical circuit supporting diaphragms of such transducers in a manner such that the transducers operate at much lower resonant frequencies while reducing distortion of the diaphragms.
2. Description of the Related Art
Audio systems markets desire small flat transducers with improved low frequency output, reduced distortion and enhanced efficiency and power handling. Conventional planar magnetic acoustic transducers include a sound-generating diaphragm, which is mounted within a stator frame. An electrical trace pattern is applied to a surface of the diaphragm and is connected to receive electrical power from a suitable power source. Vibration of the diaphragm is induced by magnetic fields provided by a plurality of magnets that are mounted within the stator frame so as to be in opposing relationship to the electrical trace pattern on one or opposite sides of the diaphragm.
The array of magnets is often referred to as the magnetic motor structure of the transducer. The magnets are generally rectangular bar type magnets that are mounted so as to be in parallel relationship to a plane of the diaphragm. The pole positioning or arrangement of the magnets may vary between transducers.
As the magnet surfaces are typically planar to the diaphragm, the magnetic fields created are localized between edges of adjacent magnets or pole structures within a stator frame. As stated, single sided and double-sided magnetic motor designs have been implemented, with improved linear response being obtained from double-sided designs as the magnetic fields are not fringing on one side. The electrical conductor trace pattern and spacing is designed to ensure the electrical circuit is located in areas of maximum magnetic field strengths created by these drive magnets.
Due to the characteristics of known diaphragm materials and magnetic motor drive structures, smaller planar magnetic transducers do not exhibit efficient low frequency output and often become distorted when power levels are significantly increased. To improve efficiency, it has been proposed to widen the magnetic field profiles associated with the magnets of the motor drive structures by beveling edges of the magnets or by shaping the magnets. However, such proposals have not resulted in significant increase in transducer efficiency in small sized planar magnetic speakers.